DETECTOR SYSTEMS

Abstract: A system for detecting and assessing the nature and position of an object passing through, and thus interrupting, one or more beams (13), which system comprises means (14) arranged to generate a matrix of beams (13) intersecting each other, to form a net-like pattern of beams, and means arranged to generate information relating to any beam(s) (13) interrupted by an intruding object and to supply such information to an analyser arranged to determine therefrom, to a suitable approximation, both the nature and position of the object which has interrupted the beam(s) (13).

Description: DETECTOR SYSTEMS DESCRIPTION This invention relates to detector systems and concerns, in particular but not exclusively, such systems which may be useful in detecting the presence of an intruder gaining or attempting to gain access to a secure area. For many reasons, it may be that an area - a building, perhaps, or some land - needs to be kept secure in the sense either that no unauthorised persons can enter it or that, if they do, their presence is detected so that some appropriate action can be taken. Such an area may typically form a compound, a fence of some sort defining the area within which there are articles and buildings to which only certain persons are permitted access. It is evident that keeping an area secure will, for the most part, involve detecting the presence of an intruder within that area, and especially of determining an intruder's passage into the area, so that action can be taken before the intruder implements his purpose. Much effort has been expended in devising detector systems which will note and warn about an intruder crossing the perimeter or boundary of a secure area. Such systems range from the simplest, for example, trip wires just above the ground surface, through to the more complex, for example, a multiplicity of pressure pads just below the ground, and on to the extremely sophisticated, such as, a vertical array of horizontal parallel laser beams extending between spaced posts to form a "wall" of laser radiation, with each system having its advantages and disadvantages. - Indeed, even the most complex of present-day laser barriers can be triggered by something as unintruder-like as an animal or a wind-borne plastic bag, without the system operator being able to determine by what, or even where, the perimeter of the secure area has been breached. The present invention seeks to solve this problem by providing a "light"-beam-based, preferably an infra-red (IR) laser-based, detection system which enables the nature, such as, the shape and position of an "intruder" to be assessed more positively and with greater accuracy. It proposes that there be used a matrix of beams crossing each other, to form a net-like pattern of beams, and that information about which beams are broken when blocked by an intruding body be supplied to an analyser which determines therefrom, to a suitable approximation both the general shape and the position of the body which has interrupted the beam pattern. In one aspect, therefore, the invention provides a detection system for detecting and assessing the nature and position of an object passing through, and thus interrupting, one or more beams, which system comprises means arranged to generate a matrix of beams intersecting each other, to form a net-like pattern of beams, and means arranged to generate information relating to any beam(ε) interrupted by an intruding object and to supply such information to an analyser arranged to determine therefrom, to a suitable approximation, both the nature and position of the object which has interrupted the beam(s). The detection system of the invention is preferably an electromagnetic, such as, a light. beam-based detection system, .that is to say, it is a system which uses beams of electromagnetic radiation extending from one or more transmitter thereof to one or more receiver thereof. The beam may, in principle, be of any suitable electromagnetic radiation but, in practice, it is most preferably light of a frequency which is invisible to the human eye, more specifically infra-red (IR). Moreover, while the source of radiation might be any transmitting device capable of providing a sufficiently narrow and focused beam, most conveniently it is a laser beam which is not necessarily coherent, although that might have certain advantages. Other beams, such as, ultrasonic beams, may also be used as an alternative to beams of electromagnetic radiation. In the system of the invention there is used a matrix of beams actually crossing each other, to form a net-like pattern of beams. The fineness or coarseness of the net pattern may be whatever is appropriate to the size of object most likely to intersect the beams and be detected. If only large objects, such as vehicles, are to be detected, then the apertures in the net pattern may be quite large, say, several metres long and a metre or so high, but if relatively small objects, such as cats and dogs, must be seen and detected then the net apertures should be quite small, say, around 0.25 m long and 0.1 m high. For a human-sized object, a suitable aperture size is about 0.5 long and 0.25 m high. A matrix of beams can be constructed in a number of ways but one preferred way is to provide a vertically-spaced array of alternate transmitters and receivers, such as, a multiplicity of laser transmitters and receivers alternately spaced up a vertical post. Typically, six alternately located transmitters and receivers spaced roughly equally up a 2 m high post located, perhaps by 100 m or so, from a corresponding array of transmitters and receivers with each transmitter arranged to direct its beam at several, possibly each, of the receivers, either all at the same time or one after another. In this way, beams from a top transmitter of the post might extend horizontally to a top receiver of an adjacent post, the second receiver down, the next receiver down and so on, to form a fan-like set of beams, while beams from each of the other transmitters also form a similar fan as they are directed to the respective sets of receivers. Thus, all these sets of beams intersect each other, to form the desired net-like pattern in which the apertures formed thereby are roughly diamond-shaped. When the system of the invention is in use, information about which beams are interrupted when blocked by an intruding object, is supplied to an analyser which uses that information to determine the general nature and shape of what has interrupted the beams and where. Basically, the information required is little more than which beam is interrupted, and this will be quite easy if, for every beam, there is a single transmitter and receiver pair used for that beam only. However, it will normally be convenient to arrange for one or more transmitters to output several beams each and/or perhaps for one or more receivers to receive several beams. To obtain the required information about which beams are interrupted, it may be necessary to code carefully each beam, so that when it is not received by the relevant receiver, it is possible to determine exactly which transmitter/receiver pair it extended between. Thus, it might be possible to code each beam by modulating it, which is comparatively easy to do with laser beams, or, and if some form of time-based scanning arrangement is used, by knowing for which time period each beam was transmitted. The information about which beams are interrupted is supplied to an analyser which determines therefrom, to a suitable approximation, the general nature, such as, the shape and the position of the beam-interrupted object. While it could be a purpose-built hardware device, in general this analyser is in effect a software system, being a suitable program running on a computer, typically one of those modern desk-top devices known as a micro-computer. The analyser uses the data about which beams are interrupted, coupled with the fact that on this scale light travels in straight lines, to construct an area of space bounded by the uninterrupted beams within which the intruder object must lie. If the net is fine enough, then this area of space will approximate quite well to a vertical section through the object itself. Moreover, if the analysis can be carried out in real time, that is, fast in comparison to the time taken for the object to pass through the beam matrix, then there will be constructed a set of side-by-εide sections which will, when combined together, define the general volumetric shape of the object. In use, the analyser hardware associated with each pair of transmitter/receiver arrays is desirably at some central point, to which all information outputted by the pair is sent for action. Preferably, however, each post has at least the "interrupted beam identification" hardware located at the post, possibly as part thereof, and it is the data outputted therefrom, which is transmitted to a central control point for further action. Although the algorithm employed by the analyser to determine each vertical section is in practice quite complex, the basic principle underlying it is simple, and is roughly as follows:- 1) From stored data indicating the lines making up the detector "wall" along which the beams are directed to establish the matrix, there is determined the region in the matrix in which there are the most beam interruptions. 2) Working outwardly from the centre of this region, there is identified the first uninterrupted beam and the line it represents is traversed until it intersects that of another uninterrupted beam. 3) The line of the latter is similarly traversed to yet another uninterrupted beam line and so on until the first uninterrupted beam line intersection is re-encountered, whereupon the system has found all the uninterrupted beam lines immediately surrounding the object and the resulting shape "defines" the object's section and position. 4) All interrupted beam lines are tested to ascertain if they pass through the determined shape and if some do not, indicating a second object, then for these beams the analysis is repeated. 5) As the object passes through the matrix, so that its ascertained sectional shape changes with time, the several εide-by-side shapes are combined, with appropriate spatial separation, to provide a volumetric definition of the object. 6) Both after Step 4 and Step 5 the derived shapes can be tested against a library of shapes in an attempt to determine with greater certainty what the object might be. The detection system of the invention provides a greatly enhanced security system relatively free of false/nuisance alarms and capable of providing reliable information as to the general nature and position of an intruder. It is of particular value when used as part of a long range security system, such as that found at a country's border or at the perimeter of a large installation, such as, an industrial plant or a military base. Embodiments of the invention will now be described by way of illustration only and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a perimeter fence constituted by a laser beam matrix of a detector system according to the invention; Figure 2 is an elevation of a fence similar to that of Figure 1 but simpler; Figures 3A to 3E show a sequence of displays representing the various stages in the analysis of the output of a slightly simplified detector system as shown in Figure 2; Figure 4 is a view of a possible output of the system of Figures 1 and 2 in real time; Figure 5 is a diagrammatic representation of a typical arrangement of security fence posts of a detector system; Figures 6A and 6B are respective side and front elevations, on an enlarged scale, and partially cut away, of one post of the posts shown in Figure 5; Figure 7 illustrates how simple pulεe-width-coded amplitude and/or frequency modulated, transmitted beams combine at a receiver of the εyεtem; Figures 8A and 8B are respective block diagrams of circuitε for tranεmitter and receiver circuitε operating with amplitude modulated beam pulεeε; and Figures 9A and 9B represent a flow chart diagram of a corresponding software algorithm for proceεεing the εignalε only from the beam receivers of the system. A detector syεtem, as shown in Figure 1, compriseε a fence conεiεting of a multiplicity of poεtε 11 (only two are εhown) which εurround an area to be kept secure. Each post 11 carrieε on itε εide adjacent one of itε neighbouring poεtε a εpaced linear array of a multiplicity of alternate laser transmitters 12 and receivers 14. Each tranεmitter 12 directε a laser beam 13 on to the receivers 14 on the adjacent poεtε 11. In Figure 1 each tranεmitter 12 iε εhown emitting a laser beam 13 on to each of the receivers, whereas in Figures 2 and 3 the laser means 13 are directed on to only some of the receiverε 14. The laεer tranεmitterε/receiverε 12, 14 are cloεer together in the region of ground level than nearer the tops of the poεtε 11, in order to optimiεe detection of low-level intruding objectε, εuch as, a crawling person or a person offering the smallest profile to the plane of the fence, namely, by a rolling action. It will be seen that the criεε-croεεing beamε 13 provide a matrix or network, having comparatively εmall apertureε therein. It would be difficult, if not impoεεible, for any object of the same general size as that of the apertures to paεε through the matrix without breaking one or more of the beams, even if positioned very carefully. The laεer tranεmitterε 12 and receiverε 14 are supplied by a power arrangement (not εhown) and beam coding means (also not εhown) and the receiverε paεε their output to a beam analyεer (alεo not εhown). Figure 2 shows a simpler arrangement of poεtε 11, transmitters 12 and receivers 14 but, otherwise, much the same as that of Figure 1. The sequence of Figures 3A to 3E representε the variouε εtages in the analysis of the output of a slightly more simplified detector εyεtem light beam arrangement. There iε εhown in each caεe two poεtε 31, 32, one carrying a εpaced linear array of six transmitters 12 numbered 0 to 5 and the other carrying a corresponding array of detectors 14, these making a matrix of criεε-croεεing, interεecting beamε 13. For clarity all theεe are only referenced in Figure 3A. In this sequence tranεmitter 0 directε beamε on to receiverε 0, 2 and 4, while tranεmitterε 1 to 5 direct beamε reεpectively on to receiverε 1, 3 and 5; 0, 2 and 4; 1, 3 and 5; 0, 2 and 4; and 1, 3 and 5. Figure 3A shows the full complement of uninterrupted beams 13. Figure 3B, however, shows an opaque object depicted by the line 33, placed in the matrix so as to interrupt some of the beamε, the interrupted beamε 34 being εhown aε daεhed lines. There are, however, a number of uninterrupted beams, and thoεe 35 closest to the area around the object 33 have been emboldened in Figure 3C and in Figure 3D, there being εhown only those parts of those lines 35 which directly surround the object 33. It will be clear that the space in Figure 3D defined by the closeεt beams 35 must "define" the furthest posεible boundarieε of the εectional shape of the object 33. Moreover, by applying pattern matching techniques it can be guessed that the most likely actual εectional shape for the object 33 is in fact the smaller area 36 εhown hatched in Figure 3E. Imagining that the object 33 iε in fact εomething which iε actually paεεing through the beam matrix, either into or out of the plane of the paper, and taking a number of εimilar "readingε" from the receiver output aε thiε paεεage occurε, there can be conεtructed a view of the object aε a whole. Such a poεεible view iε εhown in Figure 4, which revealε that the object waε a camel and that the view of Figure 3E correεpondε to the εection on the line E-E in Figure 4. The analyεiε of the interrupted beam receiver information is effected aε follows:- 1) The matrix of intersecting beamε iε εcanned to discover the region containing the greatest number of intersecting beam interruptions. Thiε region iε known aε the Primary Intruder Outline (PIO) . 2) The "centre" of thiε region iε then calculated. One of the interrupted beams iε then εcanned from thiε "centre" outwardly until an interεection with an uninterrupted beam iε encountered. Thiε firεt uninterrupted beam iε then εcanned until it croεεes a second uninterrupted beam. Thiε intersection iε εtored aε the firεt point of the PIO. 3) The second uninterrupted beam iε then εcanned until it encounters a third uninterrupted beam and thiε interεection iε εtored aε the second point of the PIO. For the purpoεeε of calculation, the laser posts themselveε are conεidered to be uninterrupted beamε. Alεo two uninterrupted horizontal beams are assumed to exist, one above the topmost actual beam and one below the lowest actual beam. 4) This procesε iε continued until the firεt point iε encountered again. The complete outline of the εhape within which the intruder exists can then be plotted on a screen. The direction of scan of an uninterrupted beam is determined by the equation of the beam and the co-ordinates of the "centre". 5) Examination of all uninterrupted beamε is then performed to ascertain whether any interrupted beams exist which do not paεε through the PIO. If any are found, the above procedure iε repeated to determine the Secondary Intruder Outline. 6) Once the PIO haε been determined, further examination of intersections of the interrupted beamε within thiε outline are made to calculate the oεt probable Primary Intruder Poεition and Shape. The Secondary, Tertiary, etc. Intruder Outlineε are similarly procesεed if applicable. 7) Analyεiε of the εequence of Intruder Outlineε enhanceε poεition calculations and provideε low reεolution front and εide profileε of any intruder. Referring now to Figure 5 of the drawings, there iε εhown a diagrammatic representation of a typical arrangement of εecurity fence poεtε for the inventive detector εyεtem, which coverε, εay, a fence εector of ten kilometres in length. In this particular embodiment, only three fence poεtε 11 are εhown. Each poεt 11 includeε control electronicε, power converter and battery back-up and a communicationε link (not εhown) for the associated laser tranεmitterε and receiverε. Local or diεtributed power iε provided for those electronic components and circuitry via supply lines 51. Reεpective control proceεεorε for the laεer ■ fence configuration of Figure 5 provide an interface to secondary εyεtemε, together with a redundant link 53 for each εector, which allows tranεferal back-up and remote reporting. A portable teεt inεtrument iε εhown at 54 for periodic teεting of the electronic componentε and circuitry of each fence poεt 11. In reεpective Figureε 6A and 6B, partial front and εide views of a portion of each fence post 11 are shown. Each post 11 includes in the interior thereof, an environmental housing 61 with an access panel 62 secured thereto by captive fastenerε 63. An environmental εeal 64 iε alεo provided for the cover 62. Alεo accommodated in the environmental housing 61 iε the control unit an aεεociated circuitry at 65, together with an aεsociated wiring loom 66 and asεociated cable glands 67, 68. A power supply controller 69 iε connected to the electronic control unit 65 via εuitable cabling 70. Reεpective AC and DC key εwitch iεolatorε 71 and 72 are alεo provided, with aεεociated cabling and cable glandε. The power supply controller 69 has a series of power supply εtatuε lampε 73 which can be viewed externally through a clear panel 74 in the removable acceεε cover 62. A pair of vertically εpaced laεer tranεmitter and receiver 81, 82 are located above and below a low maintenance battery arrangement 83. Power/data cableε 84 connect the battery assembly 83 and the tranεmitter 81 and receiver 82 to the control unit 65 via the DC isolator 72, the power supply controller 69 and the interconnecting cable 70. Figure 7 εhowε how simple pulεe width coded amplitude and/or frequency modulated, transmitted laser signals combine at a receiver as a pulεe frame. It iε the repetition rate of these frames which iε choεen to detect the faεtest moving anticipated intruder by the presence or absence of one or more coded laser pulseε. The εignal from each tranεmitter 12 (Figureε 1 and 2), 81 (Figures 6A and 6B) may be a εequence of smaller duration pulεes whose time relationship describe a data value similar to the way in which data is transmitted serially between aεsociated computers of the system. Hence, the lasers may be used for data communication purpoεeε by uεing the εyεtem aε a multiplexed data channel, the abεence of individual timed data ele entε providing the beam interruption information. Figureε 8A and 8B εhow reεpective laεer tranεmitter and receiver block circuit diagramε for amplitude modulated pulεeε, εuch aε thoεe εhown in Figure 7. Proviεion iε included in the tranεmitter circuit of Figure 8A for the control of the output power in order that the εyεtem can compenεate for varying environmental conditionε of operation. In thiε particular embodiment, the receiver circuit includeε proviεion for gain control in order that the system can compenεate for varying environmental conditionε and to maximise the εignal-to-noiεe ratio. The combination of gain and power controlε with signal level comparatorε formε a εucceεεive approximation, analogue-to-digital converter for signal level detection and correction. In thiε . εimplified arrangement, a comparator with hyεtereεiε iε uεed to provide clean εignal edgeε for pulεe width meaεurement. Additional proviεion for the control of power εupplieε an opto-iεolated interfaces between system modules iε deεigned εuch that the relevant safety requirementε can be met. Generally, beam interruption information iε communicated to a controlling micro computer for the syεte which proceεεeε received information from adjacent poεts 11, enunciates, if necessary, the alarm and, after implementing the software algorithm εhown in flow diagram form in Figureε 9A and 9B, diεplayε the reεultε in graphical form to aεsiεt the operator in determining the nature and/or size of the intruder, as described previously above.

Claims: CLAIMS 1. A εyεtem for detecting and aεεeεεing the nature and poεition of an object passing through, and thus interrupting, one or more beams, which εyεtem compriεes means arranged to generate a matrix of beams intersecting each other, to form a net-like pattern of beams, and means arranged to generate information relating to any beam(ε) interrupted by an intruding object and to εupply such information to an analyser arranged to determine therefrom, to a suitable approximation, both the nature and position of the object which has interrupted the beam(s). 2. A system according to claim 1, which is an electromagnetic beam-based detection system. 3. A system according to claim 1 or 2, wherein the or each beam is a light beam of a frequency invisible to the human eye. 4. A εyεtem according to claim 1, 2 or 3, wherein the or each beam iε a laεer beam. 5. A system according to claim 1, wherein the or each beam is an ultrasonic beam. 6. A εyεtem according to any preceding claim, wherein the or each beam extendε from a tranεmitter to a receiver thereof. 7. A system according to any preceding claim, wherein the net-like pattern generated by the or each beam iε of a fineneεε or coarεenesε appropriate to the εize of the object most likely to intersect the beam(s) and be detected. 8. A εyεtem according to any preceding claim, wherein the matrix of beamε iε generated by a vertically-εpaced array of alternate tranεmitterε and receiverε. 9. A εyεtem according to claim 8, wherein the transmitters and receivers are spaced alternately up a post located from a corresponding array of transmitters and receivers,with each transmitter arranged to direct its beam at several of the receivers of the corresponding array either at the same time or one after another. 10. A system according to claim 9, wherein each transmitter is arranged to direct its beam at each of the receiverε of the corresponding array, to form a fan-like set of beamε, εuch that all sets of beams intersect each other to form the net-like pattern in which the apertures formed thereby are roughly diamond-shaped. 11. A system according to any preceding claim, wherein one or more transmitterε is or are arranged to output several beams and/or one or more receivers are arranged to receive several beams. 12. A system according to any preceding claim, wherein each beam is coded, so that when a beam iε not received by the relevant receiver, it is poεεible to determined exactly between which tranεmitter/receiver pair it extended. 13. A εyεtem according to claim 12, wherein each beam is coded by modulating it. 14. A εyεtem according to any preceding claim. wherein information about which beams are interrupted, iε εupplied to the analyεer which determineε therefrom, to a εuitable approximation, the general nature of the beam-interrupted object. 15. A εyεtem according to any preceding claim, wherein the analyser comprises a software system. 16. A εyεtem according to any preceding claim, wherein the analyεer iε arranged to uεe the information relating to which beams are interrupted, to conεtruct an area of space bounded by the uninterrupted beams within which an intruding object lies. 17. A εyεtem according to claim 16, wherein the net¬ like pattern is εufficiently fine to provide an area of εpace which approximateε to a vertical section through the intruding object. 18. A syεte according to claim 16 or 17, wherein the analyser is arranged to carry out its analysis of the generated information relating to any interrupted beam(s) in real time, to conεtruct a εet of εide-by- εide εectionε which, when combined together, define a general volumetric εhape of the intruding object. 19. A εyεtem according to any preceding claim, wherein the analyεer compriεeε hardware which iε aεεociated with each of a plurality of pairs of beam tranεmitter/receiver arrayε and iε located at a central point to which all information outputted by the pair iε εent for proceεεing. 20. A εyεtem according to any of claimε 1 to 18, wherein the analyser compriseε hardware which iε asεociated with each of a plurality of pairs of beam transmitter/receiver arrays and wherein at least the hardware for identifying interrupted beams is located remote from a central control point, the information outputted from the interrupted beam identification hardware being transmiεsible to the central control point. 21. A system according to any preceding claim, wherein the analyser is arranged to determine vertical sectionε of interrupted beamε of the net-like pattern of beams using an algorithm.

Inventors: LATTA DAVID WILLIAM, LATTA, DAVID, WILLIAM
Applicants: INTELSEC SYSTEMS LTD, LATTA DAVID WILLIAM, INTELSEC SYSTEMS LIMITED, LATTA, DAVID, WILLIAM
Application year: 1994
Main classification: G01V9
IPC codes: G01V8, G08B13